1. Field of the Invention
This invention relates to equipment useful in transferring fluids. In particular, it relates to multiple line, fluid swivels capable of transferring fluids to and from ships, tankers and other sea-going vessels.
2. Description of the Prior Art
During the past several years the search for oil and gas in offshore areas has greatly expanded and has now progressed into deep, rough waters such as in the North Sea. To facilitate production of oil and gas from remotely located offshore fields, complex tanker mooring systems, which serve as centralized production sites for the entire field, have been developed. Normally, a bundle of flexible fluid lines extending from a subsea location to the mooring site permits the transfer of fluids between a moored tanker and the subsea location. For example, certain fluid lines may be used to convey oil and gas into the tanker while other fluid lines may be used to inject liquids or gases back into the field for the purpose of well stimulation or storage.
Under the influence of wind and waves, a tanker will tend to move in various directions about a mooring site. To permit the tanker to rotate and move freely without causing twisting or entanglement of the various fluid lines to which the tanker is attached, it is necessary to provide a swivel mechanism to connect the fluid lines to the mooring site. Furthermore, since a plurality of fluid lines are involved, it is necessary that such a swivel have the capability of accomodating multiple lines.
Multiline, fluid swivels have been developed for offshore oil field applications. (See, for example, U.S. Pat. Nos. 2,894,268 and 3,698,433.) However, most of the multiline swivel designs known in the art involve the use of stationary pipes which extend from the flexible fluid lines and which elbow into and mate with individual swivel headers. The headers are normally mounted together in a vertically stacked arrangement. Rotatable manifolds, peripherally positioned on the headers, provide fluid communication with the stationary pipes and permit free rotation of external fluid lines. The limitation of this type of design, is that it is primarily intended for low or moderate pressure operation. High pressure fluids within the stationary pipes of this type of swivel tend to displace or move the pipes at the point at which they elbow into the manifolds, thereby creating excessive tensile loading on the swivel headers. Such excessive loading can ultimately lead to leakage across fluid seals and failure of the swivel. Thus there is a need in the art for a multiline swivel capable of handling the transfer of high pressure fluids.